How is it that we breathe in oxygen, when the air consists of many gases?
We breathe in air as a whole into our lungs. The air consists of all sort of gases with niotrogen as 78 % and oxygen around 21 % depending on the surrounding environment. In our lungs this air comes in contact with the blood which carries a compound named heamoglobin. Basically it is a ferrous compoound and has an ability to react with oxygen and form oxy-haemoglobin. The oxyhaemoglobin is taken then by blood to entire body cells where it supplies oxygen and takes carbondiaoxide (and becomes carboxy-haemoglobin) with it back to the lungs. In lungs the same process is again repeated. The Carboxy-haemoglobin changes into oxyhaemoglobin i.e it releases carbondiaoxide and takes oxygen.